Ferrite phase shifter having casing-supported thin-foil waveguide, with magnetising pole pieces penetrating the casing



1963 J. CHANDLER, JR.. ETAL 3,101,458

FERRITE PHASE SHIFTER HAVING CASING-SUPPORTED THIN-FOIL WAVEGUIDE, WITH MAGNETISING POLE PIECES PENETRATING THE CASING Filed Aug. 4, 1958 2 Sheets-Sheet 1 WWW A I 2 g? /W 46 g 46' 12 4 4 14 V4 ///f//j I W INVENTORS Joy/v CHANDLHQJR, [5575? C. Hour #0 JOHN 1 5 V/L 5/ 6, JK.

ATTORNEYS Aug. 20, 1963 ETAL FERRITE PHASE SHIFTER HAVING CASING-SUPPORTED Filed Aug. 4, 1958 J. CHANDLER, JR.

THIN-FOIL WAVEGUIDE, WITH MAGNETISING POLE PIECES PENETRATING THE CASING 2 Sheets-Sheet 2 A THODE Follow AMPZ/F/fk CA 77/00! HMPL lF/EE 20 BINARY FOZLOIVEA TRIGGER I I 1%. 3 o PULSE Gf/VER/ 70/? F/XED 3 SHORT 521 2 NON- SHORT MUN/m 61 07' RFC/PRO 04L 5; 0 HYBRID PHASE HYBk/D s/m-rses 54 DUMMY 1.0/40

INVENTORS Joy/v CHA/VDL 5e, JR, [ESTER C. f/ouy 0 JOHN A [,5 Va 6/6, Je.

ATTORNEYS United States PatentfO FERRITE PHASE SHIFTER HAVING CASING- SUPPORTED THlN-FOIL WAVEGUIDE, WITH MAGNETISING POLE PIECES PENETRATING THE CASING 7 John Chandler, In, Dallas, Lester C. Holly, Irving, and

John Lee Vilhig, In, Dallas, Tex., assignors to Texas Instrumentslncorporated, Dallas, Ten, a corporation of Delaware f Filed Aug. 4, 1958, Ser. No. 752,933

4 Claims. (Cl. 333-241) ing at least one ferrite element and depends upon an externally applied magnetic field for its nonreciprocalhehavior. Thesize, shape and location of the ferrite element and the magnitude of the applied magnetic field depend on the particular application and critically affectthe propagation in each direction.

The nonreciproc-al phase shifter either advances or retards the phase of the microwave signal depending upon the direction of propagation and the polarity of the externally applied magnetic field. The resonance isolator transmits energy in one direction and attenuates it in the other, while the field displacement device is used to couple energy to another waveguide in one direction of propagation but not in the other. The-latter may be used as an isolator in combination with a resistive material located Where the field is large for one direction of propagation but small for the other direction.

The nonreciprocal phase shifter may be one-of two The first uses the Faraday rotation principle in a circular waveguide with a ferrite rod placed along its.

types.

longitndinal'axis. The magnetic fieldis applied longitudinally in this type. The second type utilizes the transverse field eifect in a rectangular waveguide having one or morev ferrite elements placed in contact with one or more of its walls. It is this second type to which the preferred embodiment of the present invention is directed although the principles of the invention are applicable to the entire class of magnetic'microwave devices wherein the materials behave essentially like isotropic dielectrics in the absence of a magnetic field and become anisotropic in the presence of a magnetic field.

Briefly, a major application of a lnomeciprocal phase I I shifter is in a four port circulator. For example, a magnetron, antena, dummy load and receiver are connected via the nonreciprocal phase shifter so that reflections or 3,101,458 Patented Aug. '20, 1963 the conductive waveguide walls contain openings to receive the pole faces of the magnet which engages the ferrite-material and supplies the magnetic field. This produces a discontinuity in the waveguide walls thereby causing excessive heating since the high frequency current must flow through the high'r'esistance discontinuity. When alternate schemes are employed, the reluctance of the magnetic path is too great and hence,'are not practical.

These problems which have not been solved by the prior art are now overcome by the present invention which, for the first time, provides a magnetic microwave apparatus that is capable of high ,-frequency. operation such as in the K or V bands and that is capable of switching waveguide energy at an exceptionally fast rate, such as 4000 times a second. I

The present invention accomplishes the above by an apparatus including two rectangular waveguides, each having a pairof ferrite elements mounted on opposing pairs of walls of the waveguide. The conducting portion of the waveguide-is formed of very' thin conductive foil of material such: as aluminum for decreasing the eddy currents and for presenting a very low reluctance to the applied magnetic field which :acts upon the ferrite elements. The pole pieces of .an'ele ctrornagnet are placed in engagement with the waveguide material adjacent the ferrite elements. An outer case of non-conducting material, such as plastic, is supplied to support the foil and give rigidity to the waveguide structure. One or morecoils can be ,usedon the electromagnet to effect switching.

Accordingly, it is. a principal object of this invention to provide an improved microwave apparatus wherein one or more ferrite elements are mounted within a waveguide and are coupled to an external source of magnetic flux through a very low reluctance path, which enables operation at substantially higher frequencies and a fastiswitch ing time. I

It is a further object of this invention to provide microwave apparatus wherein a' magnetic field is selectively imreceived signals at the antenna are presented to the receiver input, but very nearly all of the magnetron power is radiated at the antenna due to elimination of substantially Pertinent prior art has a prime disadvantage in that Q pressed upon one or more ferrite elements mounted within a waveguide having a continuous unbroken surface.

Other and further objects, of the present invention will be obvious from a detailed description of the accompanying drawings. p

In the drawings:

FIGURE 2 is a section of the apparatus of FIGURE 1 .takenalong the lines 2--2;

FIGURE 3 is a functional block diagram of the electrical apparatus for exciting the magnetic circuits of FIG- .URES land 2; and Y of the waveguides 10 comprises aluminum toil 11.2 defining a pair of rectangularxguides. The minimum thickness FIGURE lis an isometric view of the microwave apparatus of the present invention;

3 of thefoil is determined by the current penetration of the signal energy in the waveguide at the transmission frequency. The thickness of the waveguide walls must be greater than the depth of this penetnation. Plastic, such as Bakelite, constitutes a backing or supporting structure 14. Ferrite elements 16 are mounted on the [foil :12 on the pair of opposing walls which are perpendicular to the E vector of the propagated wave. As illustrated more clearly in FIGURE 2, a laminated pole piece of magnetic material 18 is received in a slot provided in opposite sides of the plastic structure 14 and the pole faces of the pole piece engage the foil 12 in the proximity of the ferrite elements 16. First and second coils 20 and 22 are wound in a reverse relationship about the pole piece for providing opposing magnetic flux. It will be understood, however, that reversing of the magnetic field may be accomplished by using only one coil and reversing the current therein.

An arrangement for switching the apparatus is illustrated in FIGURE 3. As shown, a pulse source 26 drives a binary trigger 28, the latter changing state upon each successive application of an input pulse. Alternately, the right-hand and left-hand sides of the trigger 28 present a more positive voltage to cathode followers 30A and 30B,

respectively, for driving their. associated amplifiers 32A A :circulat-or embodying the principles of the present invention is shown in block form in FIGURE 4. A short slot hybrid 36 provides an equal power split and a 90 degree phase shift difference between a pair of outputs 38 and 40. A fixed phase shift device 42 is interposed between the waveguide 38 and a waveguide 43 to insure that the proper phase relationship exists between the divided transmission paths 40 and 43. The waveguides 40 and '43 :are coupled to one side of a nonreciprocal ferrite phase shifter 44, such as the one shown in FIGURES 1 and 2, and output waveguides 46 and 48 are coupled to the other side of the nonreciprocal phase shifter and to a second short slot hybrid 50.

For purposes of analysis it may be assumed that q& represents the difference in phase shifts between the two paths of the circulator when the ferrite devices have no external fields applied to them. With a magnetic field 1 applied, the phase shift through the ferrite devices are as indicated in FIGURE 4 where the arrows show the direc- 'tion of propagation. Three equations must be satisfied for this circulator:

These equations are'satisfied if 01: 02: .6 94: 1:45 and :90

Equation (1) Equation (2) Equation (3) For the power to flow from A to B, B to C, C to D, and D to A, then 0 =-0 =0 =0 This will be considered as condition I. D, D C, C to B and B to A, 01=-02=0 =04= 45. This will be considered as condition II.

As a practical application of this circulator, a magnetron 52 can be connected at A, an antenna 54 can be connected at B, a receiver 56 can be connected to C and emerge at B under condition I and at D under condition II. Signals received by the antenna connected at B will be provided at C under condition II and signals received by the antenna connected at D will be provided at C For power to flow from A to under condition I. Ihus, a combination load isolator, duplexer and microwave switch is provided.

To switch from condition I to condition II require reversing the externally applied magnetic held to the nonreciprocal phase shifter 44 and this can be accomplished by use of an electromagnet having two coils or a single coil is explained previously.

In one form of the present invention, a circulator similar to that shown in FIGURE 4 but having an antenna connected at each of B and D was designed to operate specifically 'at 34,860 plus or minus 300 megacycles per second with a switching time from one antenna to another at a rate of 4000 operations per second. Only ampere-turns were required to achieve a switching time of 80 microseconds.

The structure of this invention lends itself well to miniaturization as required by the present trend toward operation at higher and higher frequencies. Such waveguides las the one of the present invention have been constructed having inside dimensions of the order of 0.140 by 0.280 inch.

Although the specific nonreciprocal phase shifter illustrated includes two ferrite elements per waveguide, it will be recognized from the foregoing description that the invention is equally applicable to apparatus employing a single waveguide orla single ferrite element.

Substances affecting microwave energy to a considerable extent include polyirons, rferrites and powdered magnetic metal mixed with a suitable dielectric and are so well known in the art that it is unnecessary to describe the'especific materials employed in the practice of this invention other. than to say that any suitable materials can be used. Ferrite susbtances have been referred to for the purposes of illustration and description.

It will be-expressly understood that the illustrations and description are employed to teach the basic concepts of the invention and that modifications and other embodiments will be obvious to those skilled in the art from the teachings herein. Such modifications and further embodiments are within the contemplation, spirit and scope of the invention.

What is claimed is:

1. Microwave apparatus comprising a section of waveguide consisting of thin conductive foil supported on the interior of a hollow casing of nonconductive material, fernite-type phase-shifting means mounted within said waveguide, and selectively-reversible magnetic flux producing means coupled to said phase-shifting means, said flux-producing means including a magnetic core having a 7 pair of pole pieces, said pole pieces extending through said casing and contacting said foil.

2. Microwave apparatus comprising a sectionof waveguide consisting of thin conductive foil supported by a casing of nonconductive material, a flux-responsive phaseshifting device, mounted within said waveguide, and magnetic core means having a pair of pole pieces engaging said thin conductive foil adjacent said device for providing selectively reversible magnetic flux, said pole pieces being positioned in relieved portions of said casing.

3. Microwave apparatus comprising a section of rectangular waveguide consisting of thin continuous conductive foil supported on the interior of a hollow casing of nonconductive material, said casing being apertured at areas along transversely opposed faces of said waveguide to expose portions of said foil, magnetic means for providing a selectively reversible transverse magnetic field through said waveguide, said magnetic means including a magnetic core having a pair of pole pieces positioned in said apertured areas of said casing and engaging said exposed portions of said foil, and phase-shifting means positioned in said waveguide between said pole pieces and responsive to said magnetic field.

-4. Microwave switching apparatus comprising:

; ,i(a) a section of waveguide composed of thin conduc- 5 tive foil means supported on the interior surface of a hollow casing of nonconductive and nonmagnetic material, 1

(b) the casing having transversely-opposed relieved areas,

(0) flux-responsive phase-shifting material positioned Within the waveguide between the relieved areas,

(d) and selectively-reversible magnet flux producing means having pole pieces extending into the relieved areas of the casing and engaging the foil means adja- 10 cent the phase-shifting material.

References Cited in the file of this patent UNITED STATES PATENTS 2,574,790 King Nov. 13, 195d 2,776,412 Sparling Jan. 1, H957 2,849,685 Weiss Aug. 26, 1958 OTHER REFERENCES IRE Convention Record, vol. 5, part 1, July 15, 1957, pages 227-234.

IRE Transactions on Microwave Theory and Techniques,'v0l. MTT-6, N0. 3, pages 300 303, July ,11958. 

4. MICROWAVE SWITCHING APPARATUS COMPRISING: (A) A SECTION OF WAVEGUIDE COMPOSED OF THIN CONDUCTIVE FOIL MEANS SUPPORTED ON THE INTERIOR SURFACE OF A HOLLOW CASING OF NONCONDUCTIVE AND NONMAGNETIC MATERIAL, (A) THE CASING HAVING TRANSVERSELY-OPPOSED RELIEVED AREAS, 